Gas-over-oil control valve systems are often employed in process systems (e.g., off-shore drilling wells, oil fields, natural gas transmission pipeline, etc.,) in remote locations where a power source (e.g., pneumatic or electrical power) may be unavailable. Specifically, gas-over-oil control valve system use high pressure process fluid flowing through a process fluid pipeline (e.g., natural gas) to provide energy to power a control valve (e.g., an actuator) instead of, for example, pneumatic or electrical power. In particular, a gas-over-oil system includes hydraulic control fluid stored in external vessels. The hydraulic control fluid is pressurized by channeling process fluid in a transmission pipeline directly over and in contact with the hydraulic control fluid, which forces the hydraulic fluid into the control valve (e.g., an actuator of the control valve).
However, known gas-over-oil control valve systems exhaust the pipeline process fluid (e.g., natural gas) to atmosphere after the hydraulic control fluid stokes the control valve. The exhausting fluid can produce loud noise and/or high velocity flow. In some instances, the pressure vessels have relatively large volumes and require approximately 15 to 20 seconds to fill and/or evacuate the process fluid from the pressure vessels. Further, gas-over-oil systems do not employ a fail-safe mechanism because these systems typically lack a spring. Additionally, the process fluid (e.g., the gas) directly engages the hydraulic oil in the pressure vessels without a barrier therebetween. Thus, impurities in the process fluid may contaminate the hydraulic fluid and may result in damage to the actuator and/or other components of the gas-over-oil systems.